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What are Collets?

10/31/2013 4:11:19 PM | by Anonymous


Collets are holding devices that subtype of chuck that forms a collar around the object to be held and exerts a strong clamping force an object when it is tightened. This usually means of a tapered outer collar and can be used to hold a tool or work piece.


An external collet is a sleeve that is normally with a cylindrical inner surface and a conical outer surface. Collets can be squeezed against a matching taper such that its inner surface contracts to a slightly small diameter squeezing the tool or work piece whose secure holding is desired.


Often, this can be achieved with a spring collet made of spring steel with one or more kerfs cuts along its length to allow it to expand and contract. The other alternative collet design is one that several tapered steel blocks are essentially tapered gauge blocks that are held in circular position like the points of a star or jaws of a jawed chuck by a flexible binding medium such as natural rubber or synthetic.


Jacobs Rubber Flex brand is a name that most machinists would recognize for this type of collet chuck system regardless of the collet design. They have the same operating principle that is to squeeze the collet against the work piece or tool to be held and this will result in high static friction and under the correct condition it can hold quite securely.


As for the internal collet, it is used to lock telescoping tubes together. In this case, the collet is the form of a truncated cone drilled and threaded down the centre line and the collet diameter matches the bore of the inner tube by having larger end that is slightly greater than the bore while the smaller diameter is slightly less than the bore. A threaded stub and anchored at its end to the tube and then pull the collet into the tube. The increasing diameter of the collet can force the inner tube to expand and be pushed against the inner wall of the outer tube thus locking the two tubes together and often the inner tube is slotted to facilitate this expansion.


Generally, the collet is considered as a unit which consists of a tapered receiving sleeves and sometimes integral with the machine spindle. The collet proper that is usually made of spring steel is inserted into the receiving sleeve and a cap that screw over the collect as well as clamping it via another taper.


Furthermore, in shop floor terminology, the terms chuck and collet are used in contradistinction that users speak of holding a tool or work piece with either a collet or a chuck. In this context “chuck” means any type of chuck other than a collet chuck such as independent jaw chuck or scroll chuck.

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